Why is there weightlessness in space?

According to NASA's definition, microgravity describes the state in which people or objects appear weightless. The word "appear" holds the whole explanation. At the altitude where the International Space Station orbits — between 200 and 250 miles — Earth's pull is still about 90% of its surface value. What's missing on board isn't gravity, but resistance: no floor, no seat and no scale stops the fall, and it's precisely that stopping that creates the sensation of weight.

The station falls continuously toward Earth's surface. At the same time, it moves sideways at 17,500 miles per hour, and at that speed, the curve of its fall follows the curvature of the planet. So it falls around Earth instead of falling onto it. What's more, in a vacuum all bodies fall at the same rate: the crew, tools, water droplets and the modules themselves all accelerate identically. Since everything falls together, everything appears to float. A passenger in a free-falling elevator experiences the same state, though only for fractions of a second.

Acceleration on board is never zero. Residual drag from the upper atmosphere, attitude-control maneuvers, arriving spacecraft and even crew movements all generate small disturbing forces. This matters for experiments that grow crystals or observe flames without buoyancy, since they need phases that are as stable as possible. That's why the term "weightlessness" describes the crew's perception, while "microgravity" describes the measurable environment. A gravity-free space is neither of those things, and in any case doesn't exist in Earth orbit.